diff --git a/suitcase/mongo_normalized/__init__.py b/suitcase/mongo_normalized/__init__.py
index e7c1da8..d8d8a49 100644
--- a/suitcase/mongo_normalized/__init__.py
+++ b/suitcase/mongo_normalized/__init__.py
@@ -209,10 +209,10 @@ def update(self, name, doc):
                     if field in old and field in doc:
                         if old[field] != doc[field]:
                             # Allow the removal of restricted fields, but not update
-                            if doc[field] != None:
+                            if doc[field] is not None:
                                 raise ValueError(
-                                f"Field '{field}' is restricted and cannot be changed."
-                            )
+                                    f"Field '{field}' is restricted and cannot be changed."
+                                )
                 target_uid_docs = revisions_col.find({"document.uid": doc["uid"]})
                 cur = target_uid_docs.sort([("revision", pymongo.DESCENDING)]).limit(1)
                 wrapped = dict()
diff --git a/suitcase/mongo_normalized/tests/fixtures.py b/suitcase/mongo_normalized/tests/fixtures.py
index 7c77189..521c82f 100644
--- a/suitcase/mongo_normalized/tests/fixtures.py
+++ b/suitcase/mongo_normalized/tests/fixtures.py
@@ -2,7 +2,6 @@
 # intake-bluesky-mongo) to import and reuse this fixtures without importing
 # *all* the fixtures used in conftest and the dependencies that they carry.
 import mongomock
-import pymongo
 import pytest
 import uuid
 
@@ -11,12 +10,12 @@
 def db_factory(request):
     def inner():
         database_name = f'test-{str(uuid.uuid4())}'
-        uri = 'mongodb://dbroker:secret@localhost:27017/test_database?authSource=admin'
-        client = pymongo.MongoClient(uri, False)
+        uri = 'mongodb://localhost:27017/'
+        client = mongomock.MongoClient(uri)
 
         def drop():
             client.drop_database(database_name)
 
         request.addfinalizer(drop)
         return client[database_name]
-    return inner
+    return inner
\ No newline at end of file